Running off an SD card

I am trying to revive a batch of old BBBs. I put the current image on an SD card for it to live on. The original handshake of hold the user button while booting is required to make it boot from the SD card. It does that and I expanded the fs to the whole card size, etc.
But on most boots, I still have to hold that button. Back when they were fresh, it seemed like it let go of that behavior. How do I get it to just boot the SD card automatically?
Clark Briggs